GEOLOGY OF OLYMPIC NATIONAL PARK:
PART I OLYMPIC GEOLOGY

Fig. 16. Predominent geologic terranes of the Olympic Peninsula.

Theories for the Origin of Olympic Structure

Looking at and recognizing the rocks of an area and
how they formed is only the first step in interpreting the geologic
story. We would like to see how all the different rocks are related
to each other. The pattern of relationships, portrayed by a geologic
map, helps decipher the geologic structure; from this we can begin
to reconstruct the geologic history. The ultimate goal is to fit the
local geologic history into a total earth history.

The Earliest Ideas.

Some of
the observers in the Olympics thought that the bedrock of the mountainous
core, sometimes called the inner Olympics (fig 16), must be composed
of
gneiss and
granite, rocks known to be common to the cores of many mountain
ranges. The early travelers were fooled, no doubt, by the gneiss and
granite occurring as pebbles and boulders in the gravels of the major
streams on the north and east flanks of the range We now know that these
exotic rocks do not occur as bedrock in the Olympics but instead were
carried and dumped there by the Cordilleran
ice sheet as it flowed agamst and around the mountains.

Fig. 17. Formation of anticline.

One of the earliest expeditions to penetrate the mountainous interior
of the Olympics, the Press party of 1889-90, correctly determined
that at least some of the core was composed of slate and sandstone;
but their scientific observations were not taken very seriously
and they lost all of their specimens when their raft capsized on
the Quinault River.

By the
early 1900s geologists were hammering on rocks around the periphery
of the range and venturing up trails along the major drainages. Among
these early workers was Albert B. Reagan,
an Indian agent and writer with an insatiable curiosity. Reagan published
not only on the geology of the area but also on the flora, the fauna,
and, of course, the Indians.
He collected numerous Indian legends, a few of which explained, with
some basis of truth, geologic phenomena in the Olympics .

A
more modern approach to the geology was taken by Charles
Weaver, a geologist-paleontologist from the University of Washington.
Weaver studied an incredible amount of Tertiary sedimentary rock along
the western coast of the United States. In the course of this monumental
study, he examined most of the rocks on the north side of the Olympic
Peninsula and outlined the horseshoe pattern of basalt (figs. 16 and
geologic map). Today the basalt is called
the Crescent Formation (named for exposures near Port Crescent now Crescent
Bay not for its crescent outcrop pattern). In 1937, Weaver proposed
that the Olympics were part of a giant plunging arched fold, the top
of which had been eroded off. If layers of sediment are folded up in
the middle, they form an anticline,
and if the top of the anticline is eroded off, the older layers will
then appear at the surface in the center of the fold (fig. 17).

Weaver believed that the rocks of the Olympic core were older and therefore
represented the center of the anticline. This was a reasonable guess,
since most of the core rocks looked older; they were more highly deformed
and certainly harder than the peripheral rocks. He could not prove that
all the core was older, however, for although he and others had found
Eocene and younger fossils in the peripheral rocks, they found no fossils
in the mountainous part of the core.

Fig. 18. Foraminifera shells.

Meanwhile,
oil company geologists, prospecting along the western part of the peninsula,
found fossil Foraminifera,
or "forams" as they are fondly called (fig. 18). The location
of these fossils indicated that at least some of the core rocks encircled
by the arms of the basaltic horseshoe were younger than the basalt,
thus casting some doubt on Weaver's theory. In spite of this, his anticline
hypothesis has persisted into modern times.